92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Thursday, 26 January 2012: 11:00 AM
Scatterometers Reveal the Differences Between Wind and Stress Over Ocean (invited)
Room 256 (New Orleans Convention Center )
W. Timothy Liu, JPL, Pasadena, CA; and X. Xie and W. Tang

Wind is air in motion and stress is the turbulent transport of momentum. Turbulence is generated by instability caused by the vertical wind shear and buoyancy. Most people knows about winds; how it improves marine weather forecast to avoid shipping hazard, how it helps the study of monsoon and land-sea breeze, and how its convergence fuels convection that drives atmospheric circulation. But, it is stress that drives the ocean circulation and mixing and distributes heat and carbon stored in the ocean. The mixing bring short-term momentum and heat trapped in the surface into the depth to be stored over time and bring nutrient and carbon stored in the deep to surface for photosynthesis. We do not have any large-scale stress measurements until the scatterometer. Our concept of stress distribution is largely influenced by our wind concept. A scatterometer sends microwave pulses to the Earth's surface and measures the power scattered back from surface roughness. Over oceans, roughness is caused by small waves in equilibrium with surface stress, but the scatterometer has been promoted as a wind sensor (for both speed and direction). Scatterometer measurements show us that wind influences stress but does not uniquely define stress. Stress depends on ocean temperature and current that drives instability. The conventional relation between wind and stress also breaks down under the strong wind when flow separation occurs. We will use a decade long of scatterometer measurements over ocean fronts and under hurricanes to discuss the differences between wind and stress, and the accuracy of the convectional stability parameterization of wind profile. We will discuss the new understanding of wind-stress relation on ocean-atmosphere coupling.

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